The present invention relates to local oscillator signal generators and generation of local oscillator signals. More particularly, the present invention relates to a photonic local oscillator generator and the generation of a local oscillator signal therefrom in the microwave frequency band and higher.
Traditional frequency synthesis electronics are not adequate for generation of microwave and higher frequency local oscillator signals. Presently, high frequency stable electrical signals from local oscillators are obtained by multiplying a low-frequency reference (e.g., quartz oscillator) to the required high frequency, for example, 32 GHz, with several stages of multipliers and amplifiers. The resulting system is bulky, complicated, inefficient, presents high phase noise, and is costly.
Typical systems require the generation of multiple local oscillator signals followed by distribution of the signals to various points throughout an electronics rack. The cabling required for this distribution presents high loss and distortion for the local oscillator frequencies in the microwave and higher frequency bands. This often requires the duplication of costly frequency synthesis hardware at multiple points in the system. Alternate local oscillator signal generating proposals require complex frequency-locking and phase-locking electronics systems to preserve signal integrity.
Photonic generation of local oscillator signals provides improved spectral purity of the generated signal. Photonic generation is capable of producing local oscillator signals up to several Terahertz in frequency. While capable of producing these high frequency local oscillator signals, the known techniques for generating these signals produce unstable signals and require external electronic feedback loops to stabilize the generated signals.
The present invention is a photonic local oscillator signal generator which includes a plurality of parallel optical channel waveguides fabricated in a single substrate such that an evanescent tail of an optical mode field created by laser light generation in each of the plurality of waveguides overlaps with an evanescent tail of an optical mode field created by laser light generation in an adjacent waveguide. The generator also includes a pan-chromatic mirror attached to an end of the substrate. The plurality of waveguides is fabricated within the substrate such that the pan-chromatic mirror delimits one end of a laser cavity of each of the plurality of waveguides. The generator also includes a Bragg grating mirror which has a plurality of grating fringes. The grating mirror delimits a second end of the laser cavity of each of the plurality of waveguides. The grating fringes are spaced apart from each other and traverse the plurality of waveguides such that the spacing between the grating fringes, as the grating fringes traverse each of the plurality of waveguides, is different.
A local oscillator signal is generated by pumping the plurality of optical channel waveguides with a single pumping means, generating an optical mode field in the laser cavity of each of the plurality of waveguides, each of the optical mode fields having a unique center frequency, phase locking the optical mode field of adjacent ones of the plurality of waveguides, and photodetecting an interference signal resultant from the phase locking of the adjacent optical mode fields.
The present invention provides a local oscillator signal generator for generating local oscillator signals ranging in frequency from a few megahertz to several terahertz.
The present invention also provides a local oscillator signal generator with improved resistance to environmental variations.
The present invention further provides a local oscillator signal generator that generates highly stable signals.